e-News - August, 2006 Printable version
Table of Contents

. VB/VGF process simulation
. Search of thermo-physical crystal properties
. FEMAGSoft simulation software
. Forthcoming events. 		 
 
Dynamic simulation of a simplified Vertical Bridgman process. Thermal isolines are separated by 50K. The melt-crystal interface is highlighted.
   
VB/VGF process simulation

Numerical simulation is the best tool to optimize the design of high-temperature, high-pressure crystal growth furnaces. This technique is devoted to assist the process developers by providing accurate prediction of the effect of changes of the hot-zone components, of the furnace dimensions and materials, and of the operating conditions on the grown crystal quality.

In particular, FEMAG-VB software is a high-tech tool for Vertical Bridgman / Vertical Gradient Freeze (VB/VGF) crystal growth simulation.

FEMAG-VB provides the users with:
  • global heat transfer simulations, taking into account radiation and conduction in the overall furnace, and convection inside the melt and gas phases (by "global" we mean that all the furnace elements are considered and that the heat transfer modes are coupled);
  • easy-to-control fluid dynamic models for melt and gas flow computations;
  • accurate prediction of the crystallization front;
  • control of the temperature profile along the crucible or any other constituent;
  • fully time-dependent process predictions on a complex time-evolving geometry;
  • a material database containing all the physical properties of standard semi-conductors and usual furnace constituents.
By means of advanced tools (such as the ability to perform dynamic simulations or to control any temperature profile), FEMAG-VB software allows the crystal grower to further optimize his process and to expect a higher financial return from the production line by this way.
 
       
Quasi-steady simulation of a simplified Vertical Bridgman process.
The simulation includes the effect of gas convection on the heat transfer: (left) isolines of the gas flow stream function, (right) temperature isolines together with gas flow velocity vectors. 		 
 
       
The numerical simulation used for the search of unknown thermo-physical crystal properties

Whereas numerical simulation is a powerful tool for crystal growth optimization (providing optimal process parameters for given geometry and material data), another helpful application of this technique is to provide a way to determine the thermo-physical crystal properties.

For example, one of the requirements for the production of germanium substrate for successful solar space applications is linked to the properties governing the concentrations of intrinsic and extrinsic point defects as introduced during crystal pulling or wafer processing. However, these properties are not well known.

Therefore, comparing the results of numerical simulations and real experiments can help to tune the point defect diffusion and recombination parameters in order to establish and validate the complete model. 		   
     
Dynamic prediction of intrinsic point defect distribution in a germanium Czochralski-grown crystal. The vacancy concentration isolines are displayed (logarithmic scale).
Two values of the recombination coefficient, krec, are investigated.
Left ([s-1]):

Right ([s-1]):
where CI eq is the interstitial equilibrium concentration, k is Boltzman's constant, and T is temperature.
       
FEMAGSoft Simulation Software

For more than 20 years, FEMAGSoft develops simulation software dedicated to the simulation of various crystal growth processes:
  • FEMAG-CZ: dedicated to Czochralski growth simulation for semi-conductor or oxide materials.
  • FEMAG-LEC: dedicated to Liquid Encapsulated Czochralski and Vapour Controlled Czochralski growth simulation.
  • FEMAG-FZ: dedicated to Floating Zone growth simulation for semi-conductor or oxide materials.
  • FEMAG-VB: dedicated to Vertical Bridgman and Vertical Gradient Freeze growth simulation.
  • FEMAG-PVT: dedicated to Physical Vapour Transport process simulation.
More information >>


Forthcoming Events
FEMAGSoft will participate in the following events:
  • September 4 to 8, 2006: 21st European Photovoltaic Solar Energy Conference and Exhibition.

  • September 10 to 13, 2006: 5th International Workshop on Modeling in Crystal Growth.





FEMAGSoft/CESAME-UCL conference abstracts >>

 
Dynamic simulation of a Germanium-grown crystal in a simplified Czochralski furnace: (left) melt flow convection represented by the stream function (m3 s-1), (right) thermal isotherms (K).
 
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